The Killers (1946) – two shadows on the ground announce the arrival of the titular killers, stepping out from behind the diner they will enter in just a few seconds. It is one of the most excitingly scary scenes in all of film noir.
T-Men (1947) – Like a tiger lurking in the shadows, T-Men’s opening scene (after the introduction) is as cold and intimidating as it gets and it sets the mood perfectly for the most nerve-wrecking noir ever.
Sunset Boulevard (1950) – cars everywhere – the Homicide Squad – and a voice-over monologue by Joe Gillis (William Holden) make this one of the most exciting opening scenes ever.
The Big Combo (1955) – a boxing match, followed by a woman running away from two men, who finally capture her and tell her that Mr Brown wants her to see the match. Everything you need to know about The Big Combo is in those first 2 or 3 minutes.
Double Indemnity (1944) – A car speeds through Los Angeles, ignoring the STOP sign, in a foreshadowing way. Then Walter Neff (Fred MacMurray) walks into his office to tell his story. And we’re off… The narration is fantastic and every detail is on point.
Laura (1944) – That insanely awesome opening line is made even more awesome by the fact that it is spoken by noir’s most eccentric character of all time. He is then introduced to us sitting in the bathtub writing his newspaper column. Genius.
Of course, there are many, many more to choose from, but these are the ones that come to mind right now.